The overall objectives of this study are twofold. First, we intend to verify that the position of the gene locus for hereditary spherocytosis is on chromosome 12. Briefly, our data show that HS is linked to the Gm-Pi linkage group, and that this group is likely to be on chromosome 12. These conclusions are weakened by a lack of information about chromosome 8, (a second chromosome with a likelihood of having the HS locus) and by the possibility that HS may be a genetically heterogeneous disorder. By investigating more HS families, families with rearrangements of chromosomes 8 and 12, and families with biochemical variants known to be on chromosomes 12 or 18 (i.e., Glutathione Reductase, Peptidase B), both the question of the linkage of HS and its heterogeneity can be answered. Second, since we intend to collect families with hereditary spherocytosis, it seemed a small step to expand the study and include other dominantly inherited anemias in the investigation. Although one form of elliptocytosis is on chromosome 1, a second type may be recognized by its lack of linkage with Rh. Obviously the linked variety of elliptocytosis is genetically distinct from spherocytosis. However, the unlinked type and perhaps certain forms of the probably heterogeneous stomatocytosis could be allelic types of hereditary spherocytosis. Such a hypothesis can be quickly discarded by the demonstration of a lack of linkage with Gm.